An engine usually runs with all of its cylinders. However, when this engine operates at low or medium loads, the engine efficiency is degraded by the friction and throttling contribution increase in the case of gasoline type engines.
It has already been proposed to operate only part of the cylinders of this engine and to make the remaining part inactive, which allows to increase the load on the cylinders remaining active.
Fuel injection is therefore cut off only in the cylinders to be deactivated. This allows to favour fuel consumption reduction by injecting the necessary fuel only into the cylinders required for energy production for an engine operation at low or partial loads.
Thus, by way of example in the case of a four-cylinder engine, two cylinders can be made inactive, which allows to obtain combustion in the active cylinders for each crankshaft revolution.
Although this type of engine operation is satisfactory, it however involves some drawbacks that are in no way insignificant.
In fact, since the exhaust and intake valve lift laws remain unchanged, the various intake and exhaust phases of the inactive cylinder(s) will lead to dysfunctions.
Thus, when the supply of fuel to the cylinder to be made inactive is stopped, no fuel mixture is achieved in the combustion chamber and only a volume of air is present after the intake phase. This volume is then going to be compressed during the phase of this cylinder that corresponds to its compression phase. During the phase that follows this compression phase, and in the absence of combustion, the piston is not subjected to a force resulting from the expansion of the burnt gases and it only expands a volume of compressed air. This generates cooling of the air contained in the cylinder and this temperature decrease is transmitted to the cylinder wall. This cooling is also transmitted to the entire exhaust line during the exhaust phase of the inactive cylinder with a motion of the piston from the bottom of the cylinder to the top of the cylinder. During this motion, the cold expanded air is driven by the piston towards the exhaust valve and it travels the entire exhaust line while causing cooling thereof as well as dilution of the exhaust gases. This can pose considerable problems as regards the various depollution means this line is equipped with, notably catalysts.
Furthermore, when the initially deactivated cylinders are restarted, they are cold and they therefore make it difficult to achieve combustion of the fuel mixture.
The present invention aims to overcome the aforementioned drawbacks by means of an engine of simple and economical design allowing to further reduce the fuel consumption while maintaining the temperature of the cylinders.